The slim, young woman strolls into Washington area banks, usually wearing sunglasses, a baggy gray sweater and a stylish gray beret. She also carries a shoulder bag or tote bag and, in her left hand, a brown sock with a toe that bulges with a lemon-shaped object.

When she walks up to a teller she presents a note stating the lemon-shaped object is a hand grenade and demanding money.

She usually gets a lot of cash, and so far she has eluded police.

Yesterday, the woman investigators have dubbed "the lady in gray" and "the hand grenade lady" did it again, this time at the First American Bank of Virginia branch at 6949 Commerce St. in Springfield. She walked away with what police described as a duffel bag containing "a substantial amount" of money.

It was the sixth time she has robbed an area bank since August, the second time in four days, clearly irritating police.

"We're starting to take it personally," said Fairfax County officer Connie Curran, only half joking.

The six robberies, five of them in Fairfax, are extraordinary, police say, because the person committing them is a woman, because she claims to have a grenade, and because she has managed to pull off such a long string using the same technique with such a casual -- and predictable -- style. What's more, she has managed to rob all six banks using the same note -- one that she demands back with the cash.

The six robberies -- two in Annandale, one near Seven Corners, one in Wheaton, one at Baileys Crossroads and yesterday's in Springfield -- have been committed in pairs. The first two came four days apart in late August, the second two came two days apart a month later, and the most recent were four days apart, last Thursday and yesterday.

Fairfax prosecutor Robert F. Horan Jr. said the county had not had a female bank robber since the1960s. "It's not a woman's crime," he said.

No other area police officials could recall any past bank robber claiming to have a hand grenade. Yesterday was the first time the woman has struck before noon; the previous robberies all were committed between 2 and 4 p.m.

Police say she spends two to five minutes in the banks she robs and arrives and leaves without hurrying. Her note specifies the drawer from which she wants money and lists denominations of bills she wants, police said.

She holds the sock in which she claims to have the grenade in her left hand, police said, and almost never speaks.

Only once in the series of robberies did things go awry. At the robbery of a First Virginia Bank branch at Baileys Crossroads Thursday, a teller told the woman there was no money in the drawer she specified.

The woman insisted, police said, and when the teller opened the drawer to show the woman it was empty, the robber left the bank empty-handed. It was the only one of the six in which the woman has not gotten away with "a substantial amount" of money.

Police refuse to say whether they know who the woman is or whether a warrant has been issued for her arrest, but they have released pictures of her taken by bank cameras.

Fairfax police spokesman Warren Carmichael said yesterday additional investigative resources had been thrown into trying to capture the woman, but declined to elaborate.

Yesterday was the second time the woman has robbed a First American branch. She has also robbed two First Virginia Bank branch offices, a Sovran Bank branch and a Central National Bank branch.

In her first two robberies, in late August, the woman wore purple sneakers with white stripes, police reported, a fashion she has since abandoned. Police say that since then she has worn black shoes.